The present invention relates to a wireless IC tag using a radio frequency of sub-microwave band and having no battery. A detailed description is given of a conventional wireless IC tag using the radio frequency band and having no battery in Shinichi Haruyama, xe2x80x9cTechnologies for microwave ID card systemxe2x80x9d, the supplement of Japanese magazine xe2x80x9cTransistor-Gijujtsuxe2x80x9d published by CQ Publishing Co. Ltd., pp. 21-29, May 1992. In a rectenna (circuit comprising an antenna and a rectifying circuit) of a wireless IC tag described in the paper, there is introduced an antenna as shown by FIG. 1 comprising a series connection of a half-wavelength resonator and a shottky barrier diode. FIG. 1 shows the rectenna circuit, numerals 1 and 2 designate quarter-wavelength antennas, numeral 3 designates a shottky barrier diode, numerals 4 and 5 designate inductors, numeral 6 designates a condenser and numeral 7 designates an output terminal. Microwave power received by the xc2xc wavelength type antennas 1 and 2 is rectified via the shottky barrier diode 3 and the inductor 5 and is accumulated in the capacitor 6 as direct current and is outputted from the output terminal 7 as necessary. Further, there is described an example of utilizing a rectangular microstrip-patch antenna in AIM Japan, xe2x80x9cTechnologies and applications for data carrierxe2x80x9d published by THE NIKKAN KOGYO SHIMBUN, LTD. pp. 22-25, October 1990. FIGS. 2A, 2B and 2C show the example of the rectangular microstrip-patch antenna in which FIG. 2A is a plane view, FIG. 2B is a side view and FIG. 2C shows a rear face. In FIGS. 2A, 2B, 2C, numeral 8 designates a rectangular patch, numeral 9 designates a dielectric member, numeral 10 designates a ground conductor, numeral 11 designates a feed line and numeral 12 designates a feed point. A microwave signal inputted from the feed line 11 is resonated at a frequency determined by a length xe2x80x9clxe2x80x9d of a side of a square shape including the feed point 12 of the rectangular patch 8. According to these antennas, when the losses of the member is reduced to reduce loss of the antenna, the Q of the resonating circuit becomes high and a matching frequency band is narrowed. When the Q of the resonator is increased, it is difficult to widen the matching frequency band of the antenna.
According to a wireless IC tag, voltage generated by rectifying current is changed in accordance with a distance between the wireless IC tag and an interrogator antenna and when the wireless IC tag becomes proximate to the interrogator antenna, the rectifying voltage is rapidly elevated. Therefore, in view of the withstanding voltage of an IC, a voltage value is devised to be maintained at a predetermined value or lower by a voltage limiter comprising transistors connected in multiple stages in Japanese Laid-open Patent (Kokai) No. Hei 8-185497. Further, a result of communicating with the wireless IC tag is produced by data of the wireless IC tag absorbed from the interrogator.
With regard to a structure of a dipole antenna for electrically connecting and packaging an antenna of a wireless IC tag and an IC circuit, in xe2x80x9cmanufacturing method for wireless tagxe2x80x9d disclosed in Japanese Laid-open Patent (Kokai) No. Hei 10-32214, there is described a method of mounting a structure in which an IC is attached to a strip-like antenna having a lead frame structure and an IC attaching portion thereof or a total thereof including the antenna is integrated by a mold technology such as transfer molding.
According to the conventional technologies, it has been difficult to widen a matching frequency band by promoting a sensitivity of the antenna of the wireless IC tag. It is an object of the present invention to achieve wide band formation without deteriorating the sensitivity of an antenna to thereby facilitate to manufacture the antenna by promoting the yield against the manufacturing dispersion by constituting the wide band formation of the antenna.
It is another object of the present invention to realize a circuit constitution in place of a low voltage circuit maintained at predetermined voltage by wastefully consuming current by using a transistor, a zenner diode or the like, for carrying out operation of confirming transmittance of data between a wireless IC tag and an interrogator by using power dissipated in the previous low voltage circuit without checking and determining by the data of the wireless IC tag read by the interrogator. It is another object of the present invention to manufacture of a wireless IC tag of an integrated type by filling and molding a mold material of a transfer mold or the like as a dielectric material of an antenna in a microstrip-line constitution while ensuring electric connection between IC and the antenna and ensuring also mechanical strength in the antenna for the wireless IC tag in the microstrip structure comprising a ground conductor plate constituted by a lead frame and an antenna conductor.
In order to widen a matching frequency band without deteriorating the sensitivity of an antenna of a wireless IC tag, there is achieved wide band formation by double tuning by constituting an antenna of a double tuned type in which quarter-wavelength antenna resonators in a microstrip constitution are subjected to mutual inductance coupling by an impedance element comprising a common inductor. For that purpose, there is adopted an antenna structure for grounding a middle point of a half-wavelength antenna by using a through hole conductor with a ground face of a microstrip substrate or a lead frame conductor. There is constructed an integrated structure by mechanically and/or electrically connecting IC to a surface of an antenna constituted by a lead frame conductor on a side of a ground face by using an insulating adhering agent or a conductive adhering agent and pressurizing and solidifying a mold member for transfer mold of the lead frame integrally connected electrically and mechanically to a ground conductor constituted by the lead frame conductor by a conductor for grounding at a middle point of the antenna.
In order to make the rectified voltage generated at the rectenna circuit a constant voltage, according to the present invention, an LED (Light Emitting Diode) is introduced, and constant voltage formation of the circuit is achieved by utilizing the rapid rise of the forward direction voltage of the positive characteristic of the LED. Generated power increased as the wireless IC tag becomes proximate to an antenna of an interrogator, brings about an increase in current in the forward direction of the LED, increases light emitting intensity of the LED and the circuit maintains voltage applied on an IC circuit constituted by CMOS or the like at a predetermined value. The light emitting phenomenon at this occasion indicates that the interrogator makes access to the wireless IC tag or can make access thereto. At this occasion, the IC indicates a drivable state or a driving state and constitutes a criterion of in-operation of recognizing the wireless IC tag or finish of operation by a congestion control. Further, by setting and disposing a logic circuit in the IC circuit, the logic circuit can be used in various signals for positively controlling the light emitting state of the diode and knowing the state of the wireless IC tag via the logic circuit.
By press forming of a lead frame flat plate, the lead frame flat plate is formed in a shape of a cross having a connection conductor with a ground conductor at a middle point portion of a half-wavelength antenna formed in a short strip further formed with a connecting portion for connecting to match with the IC circuit between a middle point of any of the sides and an opening end of the antenna in the longitudinal direction of the antenna, further connected with a circuit of the wireless IC tag or a terminal for inputting/outputting signal of IC arranged at the middle point portion of the antenna by a technology of wire bonding or the like and at the same time, by connecting the circuit of the wireless IC tag or the ground terminal of the IC to the antenna conductor by the technology of wire bonding, the antenna portion is formed. From the lead frame flat plate constituting the ground conductor of the antenna of the microstrip-line formed by the same lead frame flat plate, there is formed a ground conductor portion in a shape of a box having an area wider than the face of the antenna and a shallow depth by a hexahedron structure one face of which is opened and which is press formed and the ground conductive portion is mechanically and electrically connected thereto at a connecting conductive portion of the ground conductor of the antenna portion such that the circuit or the IC of the wireless IC tag constitutes a face on the side of the ground conductor and such that the antenna portion and the ground conductive portion are kept in parallel with each other and a mold material used in transfermolding or the like is filled in a gap of parallel portions of the antenna and the ground conductor portion and the total is formed integrally.
Further, the wireless tag constituted by the microstrip-line receives radio waves from the antenna side and accordingly, the ground conductor on the rear face may be arranged to be opposed to the radio wave radiating side. Therefore, in the case in which the wireless tag is arranged to a distributed article or the like, the ground conductor side may constitute an adhering face.
These and other objects and many of the attendant advantages of the invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings.